Shaped catalyst particle for use in hydroprocessing of petroleum oils

ABSTRACT

Petroleum-derived feedstocks are treated at elevated temperatures and pressures in the presence of hydrogen and in contact with a bed of porous catalytic particles. In accordance with the invention, each of the catalytic particles is specially shaped as a cylinder of polylobate cross-section having bluntly rounded, concave, interlobular interstices and in conformity with a selected combination of values of three defining parameters. The particle shape is further characterized as being substantially straight-sided and as having a geometric surface-to-volume ratio in the range of about 40 to about 95 in  2  /in 3 . When the catalyst particle cross-section is selected to be circumscribed by a rectangle, the shorter side of the rectangle is about 70% as long as the longer side of the rectangle for all preferred combinations of values of the defining radial parameters. Further, when the entire catalyst particle is circumscribed by a right circular cylinder of the same length as the particle, the particle itself is in contact with the cylinder along three longitudinal elements and occupies about 55% of the volume of the cylinder.

FIELD OF THE INVENTION

This invention relates generally to shaped, porous catalyst particlesuseful in fixed-bed contacting of petroleum hydrocarbon liquids andgases. More particularly, the invention relates to catalyst particleshaving a polylobate shape advantageous to the hydrotreating process.

BACKGROUND OF THE INVENTION

A number of catalyst shapes have been described in the prior art. Forexample, various catalyst particle shapes have been disclosed in: U.S.Pat. No. 2,408,164 to Foster; U.S. Pat. No. 3,966,644 to Gustafson; andU.S. Pat. Nos. 3,674,680 and 3,764,565 to Hoekstra and Jacobs. The aimof these prior art developments has been extending of particlesurface-to-volume (S/V) ratios beyond those available in simplecylindrical or spherical forms. Although the S/V ratio in a catalyticreactor may also be increased by reducing the particle size,unacceptably high pressure drops can result from this approach.

BRIEF DESCRIPTION OF THE INVENTION

The present invention overcomes the limitations of prior art particleshapes by providing a cylindric particle with a polylobate cross-sectionwherein the interlobular interstices are bluntly rounded and generallyconcave. This advantageous shape increases liquid hold-up in thecatalyst bed when the hydrotreating operation is being conducted in theusual downflow manner with the feedstock partly or entirely in theliquid phase. To the extent that the hold-up is increased, the residencetime for the hydrotreating reactions is lengthened, improving theproductivity and effectiveness of a given volume of catalytic material.Increased effectiveness permits the use of higher hydrotreating feedrates with a consequent lower unit processing cost. Configuring of theparticle in accordance with the invention produces a lower pressure dropthan is obtained in beds of particles of other shapes known to the art.Utilization of the particle shape of the invention additionally lowersthe cost of operating a hydrotreating reactor, whether the system ismaintained entirely in the vapor phase, or in the "trickle" flow mode.The catalyst shape of the invention also promotes greater scavenging ofundesirable elements such as sulfur and nitrogen than can beaccomplished by prior art particle configurations.

Finally the present invention contemplates a physically strong particlecapable of withstanding the stresses which are normally encounteredduring reactor loading and unloading operations and during exposure totypical operating conditions.

Accordingly, a general object of the present invention is to provide anew and improved particle configuration for hydrotreating catalysts andthe like.

This and other objects and features of the invention will becomeapparent from a consideration of the following disclosure.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 is a cross-sectional view of a trilobate catalyst particle shapedaccording to the prior art; and

FIG. 2 is a perspective view of a catalyst particle configurated inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now in detail to the drawing and giving first attention toFIG. 1, a catalyst particle of the prior art is fashioned with atrilobate cross-sectional shape 10 having three individual lobes 12 andindwelling, apical, interlobular interstices 14. A catalyst particlehaving such a cross-sectional shape is disclosed in U.S. Pat. No.3,990,964; and further reference to such a particle shape will be madehereinafter in connection with certain of the disclosed workingexamples.

Turning to FIG. 2 for a description of the present invention, acylindric catalyst particle 20 will be seen fashioned with across-section of polylobate, specifically trilobate, shape wherein theindividual lobes 22 are separated by concave interstices 24 which are,advantageously, bluntly rounded with greater curvature than that of thelobes 22.

An equilateral triangle ABC serves as the reference figure for selectingboth particle size and the appropriate centers of rotation for thelobe-defining radii r₂ and r₃ and the interstitial radius of curvaturer₁. Specifically, midpoints of two adjacent sides AB and AC of thetriangle ABC serve as centers for lobe-defining radii r₂. The verticesof the equilateral triangle ABC act as the centers for interstitialradii r₁ ; and the common intersection of the bisectors of the angles ofthe triangle ABC defines the center for the remaining lobe-definingradius r₃.

When the trilobular cross-section 20 is circumscribed by an imaginaryrectangle, the smaller dimension of the rectangle d₁ is selected toequal about 70% of the greater dimension d₂. With this proportiondetermined and with an initial choice made as to the desired overallsize of the particle, the radii r₁, r₂ and r₃ are selected to becompatible with the geometric relationships shown. However, radii r₂ arepreferably not less than about 0.012 inches in order to provide adequateparticle strength; and radii r₁ are made large enough to produce thelong, sweeping arc of curvature that contributes to both the physicalstrength and the streamlined character exhibited in the shape of theparticle of this invention. By also assuring that r₂ <r₃ <r₁, noparticle can have more than a line contact with any adjacent particle,thus maximizing interparticle (void) space. Preferred combinations ofthese three radial parameters, in connection with an overall cylindricheight (1) of the particle selected to be about 2.5 to 4 times thedimension d₁, have evoked particle S/V ratios of about 90 to about 95in² /in³ when d₁ is from around 0.090 to about 0.110 inches. Modern diemanufacturing techniques make the configuration of this inventionreadily achievable as well as economically feasible for extrusion on acommercial scale.

Catalyst Composition

A useful catalyst composition fashioned in the above-described shapecomprises one or more metallic components selected from Group VIB andGroup VIII of the Periodic Table of Elements, and a porous, inorganicoxide substrate supporting the metal. Suitable oxide supports include,for example, alumina, silica and silica-alumina. The combined amounts ofthe metals, calculated as oxides, are selected within the range of about2 to about 33 weight percent based on total composition. Typically, theGroup VIB metal is selected to be molybdenum or tungsten and the GroupVIII metal is selected to be cobalt or nickel. The group VIB metals arepreferably present in amounts ranging between about 4 to about 28 weightpercent calculated as the oxides; and the Group VIII metals arepreferably present in amounts ranging between about 2.0 to about 6.0weight percent calculated as the oxides.

When the support material is selected to be alumina, from 0-10 weightpercent silica may be included in the alumina matrix as a stabilizer;and depending on the catalytic application, the pore structure of thesupport material may be varied so as to obtain a desired average poresize or pore size distribution. The catalyst surface area in the porousstructure may be likewise tailored to the intended application bytechniques known in the art. Average pore size should be maintainedwithin the range of about 40 to about 600 angstroms in diameter with thesurface area between about 100 and about 400 square meters per gram.

Catalyst Preparation

A batch of alumina support was prepared in accordance with procedureswell known in the art, extruded through dies containing extrusionorifices of suitable size for producing cylindrical particles accordingto the prior art and particles of the disclosed polylobatecross-section. These particles were then calcined. This material ishereinafter referred to as "B" and was used in these forms for varioustests and in the preparation of cobalt-molybdenum and nickel-molybdenumcatalysts. These preparations were made as described in U.S. Pat. No.3,232,887 granted in the name of G. N. Pessimisis, Feb. 1, 1966, thedisclosure of which is incorporated herein by reference. Catalysts thusformulated with a combination of cobalt and molybdenum are designated"C" hereinafter for the prior art shape and "D" for the polylobate shapeof the present invention. Similarly, catalyst particles made with acombination of nickel and molybdenum are identified hereinafter as "F"and "H" for a right cylinder shape and as "G" and "I" for the polylobateshape of the present invention. Compositions of the calcined materialsare given below in Tables III, IV and V as parts of Examples 3, 4 and 5.Catalyst material designated "E" is a nickel-molybdenum formulation inright cylindrical shape, prepared as above and used as a laboratoryreference material.

In order to enhance the understanding of the invention, the followingspecific examples are given without intending to limit the invention tothe specific details set forth.

EXAMPLE 1

To demonstrate the effectiveness and superiority of the configuration ofthe present invention, when it is desired to keep pressure drop at aminimum in a fixed bed reactor, a sample of a commercial trilobecatalyst, "A", was obtained and pressure drop measurements made underidentical test conditions. Flow rates covered a range typical of vaporand gas flows in commercial reactors. The commercial trilobe and theconfiguration of the present invention were selected to be essentiallythe same in an overall dimensional sense whereby to restrict thecomparison to one in which shape was the dominant feature influencingflow. By the maintaining equality of bed void fractions while at thesame time suppressing particle size differences, the greater streamlinedcharacter of the bed shaped according to the invention is revealed.Table I shows particle physical measurements and bed pressure drop data.

                  TABLE I                                                         ______________________________________                                                      Catalyst                                                                        A          D                                                                  Commercial Present                                            Shape           Trilobe    Invention                                          ______________________________________                                        Size*                                                                         d.sub.1 (in.)   0.048      0.048                                              d.sub.2 (in.)   .051       .068                                               1 (in.)         .136       .176                                               S/V (in..sup.2 /in..sup.3)                                                                    100        94                                                 6 V/S (in.)     .060       .064                                               Bed void fraction                                                                             .39        .39                                                Apparent bulk   .95        .70                                                density (g/ml)                                                                ______________________________________                                        Percentage                                                                            Pressure Drop, in. Hg                                                                          Ratio Trilobe/                                       of Flow A          B         Present Invention                                ______________________________________                                         100**  69.6       55.6      1.25                                             90      56.0       46.3      1.21                                             80      45.7       35.4      1.29                                             70      36.2       28.1      1.29                                             60      26.7       21.4      1.25                                             50      19.0       15.2      1.25                                             40      13.7       10.6      1.29                                             30       8.8        6.6      1.33                                             20       5.0        3.8      1.32                                                                Average   1.28                                             ______________________________________                                         *Average of multiple measurements by micrometer with S and V by               calculation.                                                                  **100% is 1.74 SCFM nitrogen gas flow at one atmosphere pressure and room     temperature through a 36" long bed of particles charged with vibration to     a glass tube of 1" inside diameter. This flow is equivalent to 6377 gas       hourly space velocity. The factor designated as 6 V/S is the diameter of      sphere having the same S/V ratio as the particle.                        

The manometric measurements of the pressure drop shown in Table Idemonstrate the clear-cut advantage of the shape of the presentinvention over the entire range of flows used. On the average, thetrilobe had 28% higher pressure drop, a considerable disadvantage.

EXAMPLE 2

Since catalytic reactors in oil refining practice are commonly used inthe downflow mode with concurrent flow of gas and liquid reactants, theamount of liquid present in the bed at any instant is an importantfactor in the effectiveness and extent of contact between reactants. Letthe total liquid hold-up H_(t) be defined as H_(p) +H_(e), where H_(p)is the quantity of liquid contained in the pores of the catalyst andH_(e) is the remainder of the bed liquid. In the present discussionH_(p) may be regarded as without influence in the bed hydrodynamics.

One may divide H_(e) into components H_(d) and H_(s), the dynamic andstatic hold-up quantities that together are most important in bedhydrodynamic behavior. H_(d) may be measured by flowing liquid downthrough a tube containing the bed of particles, then at steady state,simultaneously stopping inflow and outflow, weighing the tube, thenallowing the bed to drain and weighing the amount drained. The firstvalue is used in the calculation of H_(t), the second in obtainingH_(d), and a separate pore-filling experiment gives H_(p). Statichold-up is then obtained as H_(s) =H_(t) -H_(d) -H_(p). Finally, H_(e)is determined as H_(d) +H_(s), with weight values converted to volumesby applying a value for the density of the liquid used. Table II givesresults for H_(e) at three liquid flow rates falling within a rangetypical of commercial practice. It is seen that the bed of catalystparticles according to the present invention, when compared with anequal volume bed of conventional 1/16" cylindrical extrudate, exhibitedhold-up increases of 10%, 16% and 15%.

                                      TABLE II                                    __________________________________________________________________________    Support Material                                                                        B       B                                                           Catalyst Shape                                                                          1/16" Cylinder                                                                        Present Invention***                                                                     Ratio                                            Solvent Flow Rate*                                                                      ml/100 ml bed                                                                         ml/100 ml bed                                                                            H.sub.e Present Invention/                       ml/min                                                                             LHSV**                                                                             H.sub.d                                                                          H.sub.s                                                                         H.sub.e                                                                          H.sub.d                                                                           H.sub.s                                                                          H.sub.e                                                                           H.sub.e Cylinder                                 __________________________________________________________________________    3.5  1.6  4.7                                                                              5.6                                                                             10.3                                                                             5.6 5.7                                                                              11.3                                                                              1.10                                             9.0  4.2  6.6                                                                              5.6                                                                             12.2                                                                             8.3 5.8                                                                              14.1                                                                              1.16                                             13.0 6.0  7.4                                                                              5.6                                                                             13.0                                                                             9.4 5.6                                                                              15.0                                                                              1.15                                             __________________________________________________________________________     *300-400° F. boiling range petroleum solvent, 1" inside diameter       tube, 12" deep bed                                                            **Liquid hourly space velocity                                                ***Dimensions in Table I; cylinders .063" diameter × .189" long    

Catalyst Activity

In comparing the particle shape of the present invention, when used toremove sulfur and nitrogen from a typical petroleum fraction, both lowand high pressure test conditions were employed, the low pressure testbeing concerned only with sulfur removal. A heavy vacuum gas oil wasused as the test feedstock having the following properties: 687°-1181°F. boiling range, 19.0 °API gravity, 2.9% sulfur by weight, 1620 wppmtotal nitrogen and 1.04% by weight Conradson carbon residue.

Evaluation of catalyst activity was based on rates of removal of sulfurand/or total nitrogen as calculated from analyses of feedstock andhydrotreated products using standard analytical and testing procedures.The kinetic behavior of desulfurization in the low pressure test isrepresented by the relationship by k=LHSV (s⁻¹ -S_(o) ⁻¹), where k isthe desulfurization rate, LHSV is feed liquid hourly space velocity inthe hydrotreating test, and S and S_(o) are weight percent sulfur inproduct and feed oils, respectively. In a standard test, the conditionswere kept the same for all catalysts tested and an increase in the valueof k became a direct indication of an increase in activity. It is usefulto choose one catalyst and its k value as a reference against whichothers may be compared, leading to a simple measure of relativeactivity. In the high pressure test, an appropriate rate expression forsulfur removal is k=LHSV (S⁻⁰.5 -S_(o) ⁻⁰.5) and for nitrogen removal,k=LHSV 1n (N_(o) /N) where S and S_(o) are as before, N_(o) and N arefeed and product total weight percent nitrogen and 1n is the naturallogarithm.

EXAMPLE 3

Using the "B" support alumina extruded into cylindrical shape and intothe shape of the invention, two cobalt-molybdenum impregnations "C" and"D" were made for activity testing on the heavy vacuum gas oilpreviously described. Equal volumes of each shape were charged to a dualreactor test unit, nitrogen-purged while heating to 400° F., presulfidedwith a solution of an organic sulfur compound in a light solventaccording to a standard procedure and the unit operated overnight tocondition the catalyst. The overnight and subsequent run periodsemployed hydrogen at a ratio of 2500 std. cu. ft. per bbl. of feedstock,a reactor pressure of 450 psig, a temperature of 650° F. and a feed LHSVof 3.0. Samples of product oil were taken after about 16 hours onstream, stripped free of H₂ S using nitrogen gas and analyzed for sulfurcontent. Table III shows properties of the catalysts and results of theactivity test on a relative basis. The shape of the present invention isseen to be 22% more active for sulfur removal when compared on the equalvolume basis and 24% more active when compared on an equal weight basis.

                  TABLE III                                                       ______________________________________                                                          CATALYST                                                                      C         D                                                 ______________________________________                                        Shape               1/16" Cylinder                                                                            Present                                                                       Invention                                     Weight %                                                                      CoO                 3.34        3.38                                          MoO.sub.3           14.1        14.3                                          Na.sub.2 O          .11         .18                                           Al.sub.2 O.sub.3    balance     balance                                       PHYSICAL PROPERTIES                                                           Surface Area (M.sup.2 /g)                                                                         227         217                                           Apparent Bulk       .71         .70                                           Density (g/ml)                                                                DIMENSIONS (in)                                                               d                   .063        --                                            d.sub.1             --          .048                                          d.sub.2             --          .068                                          1                   .189        .176                                          RELATIVE DESULFURIZATION                                                      ACTIVITY                                                                      Volume Basis        1.00        1.22                                          Weight Basis        1.00        1.24                                          ______________________________________                                    

EXAMPLE 4

Since nickel-molybdenum catalysts play an important part inhydrotreating hydrocarbon feeds, the support, in the form of cylindersand in that of the present invention, was impregnated with nickel andmolybdenum and designated "F" and "G". A laboratory standardnickel-molybdenum catalyst was produced commercially and designatedCatalyst "E". A high pressure activity test was then run using the heavyvacuum gas oil feed of Example 3. This run was conducted as in Example 3except for the following changes: a triple-reactor unit was used, butemploying the same reactor geometry as in Example 3; pressure was 1000psig; temperature 675° F.; and feed LHSV 1.5. Samples of product oilswere analyzed for sulfur and activities calculated relative to theCatalyst E standard. The results show that Catalyst F from support "B"cylinders gives essentially the same activity for sulfur removal as thestandard Catalyst "E" cylinders, and that shape of the present inventionexhibits an activity advantage, equal to a 22% increase over the others.Table IV gives data for the catalysts and activity results.

                  TABLE IV                                                        ______________________________________                                                        CATALYST                                                                      E      F        G                                             ______________________________________                                        Shape             1/16"    1/16"    Present                                                     Cylinder Cylinder Invention                                 Weight %:                                                                     NiO               5.53     5.14     5.17                                      MoO.sub.3         18.7     20.4     19.3                                      Na.sub.2 O        .02      .08      .07                                       Fe.sub.2 O.sub.3  .03      .03      .03                                       Al.sub.2 O.sub.3  balance  balance  balance                                   PHYSICAL PROPERTIES                                                           Surface Area (M.sup.2 /g)                                                                       170      150      154                                       Apparent Bulk     .88      .92      .88                                       Density (g/ml)                                                                DIMENSIONS (in.)                                                              d                 .060     .062     --                                        d.sub.1           --       --       .048                                      d.sub.2           --       --       .068                                      1                 .126     .162     .152                                      RELATIVE DE-                                                                  SULFURIZATION ACTIVITY                                                        Volume Basis      1.00     1.05     1.22                                      Weight Basis      1.00     1.00     1.22                                      ______________________________________                                    

EXAMPLE 5

Further examination of the activity comparison between the particleshape of the invention and conventional particle geometry was conductedby impregnating support "B" cylinders and the invention particles withnickel and molybdenum to produce catalysts "H" and "I" and running thehigh pressure test to evaluate both sulfur and nitrogen removal. Theprocedure and apparatus duplicated that of Example 4 except that onlytwo of the three reactors were used. Table V lists the properties of thecatalysts and the relative desulfurization and denitrogenationactivities. The shape of the invention is seen again to improvedesulfurization by a significant margin with a small increase evidentfor nitrogen removal.

                  TABLE V                                                         ______________________________________                                                          CATALYST                                                                      H         I                                                 ______________________________________                                        Shape               1/16" Cylinder                                                                            Present                                                                       Invention                                     Weight %                                                                      NiO                 5.20        5.38                                          MoO.sub.3           18.5        17.9                                          Na.sub.2 O          .02         .02                                           Fe.sub.2 O.sub.3    .03         .03                                           Al.sub.2 O.sub.3    balance     balance                                       PHYSICAL PROPERTIES                                                           Surface Area (M.sup.2 /g)                                                                         160         129                                           Apparent Bulk       .87         .84                                           Density (g/ml)                                                                DIMENSIONS (in.)                                                              d                   .062        --                                            d.sub.1             --          .048                                          d.sub.2             --          .068                                          1                   .149        .152                                          RELATIVE DESULFURIZATION                                                      ACTIVITY                                                                      Volume Basis        1.00        1.28                                          Weight Basis        1.00        1.32                                          RELATIVE                                                                      DENITROGENATION ACTIVITY                                                      Volume Basis        1.00        1.02                                          Weight Basis        1.00        1.05                                          ______________________________________                                    

Particle Strength EXAMPLE 6

The strength of catalyst particles is an important property whichgoverns how well the particles survive repeated reactor loading anddischarging operations and whether they are able to withstand thecompressive forces exerted on the catalyst bed during use. It is commonpractice to estimate particle strength with a device in which individualparticles are separately crushed between parallel metal plates, onestationary, the other movable and wherein the force is applied to theparticle in a side-by-side direction, i.e., across the particlecross-section for an extrudate. The test instrument is designed toregister the resistance to crushing in units of force applied up to themoment of particle failure. Information obtained in this way is usefulalthough the forces experienced by individual particles in a packedreactor bed are three-dimensional in nature.

Standard crush tests were run on a number of particles configuredaccording to the commercial trilobe and according to the patentinvention, both shapes having been extruded from support "B" alumina.Table VI shows particle dimensions and crush strength values normalizedto the customary basis of unit length. In the testing, the particleswere side-crushed in a direction perpendicular to the d₂ dimension. Bothshapes had essentially the same crushing strength as tested, althoughthe particle of the present invention, by virtue of its configuration,was structurally susceptible in this test to crushing at a lower appliedforce. This susceptibility is obvious when it is noted that theunsupported span between particle bearing points for the particle was0.042" while for the trilobe, the span was only 0.026", a considerabletheoretical advantage in this test. Since the alumina was identical forboth shapes it is believed that the trilobe failed as a consequence ofits configuration.

                  TABLE VI                                                        ______________________________________                                                        CATALYST                                                                      B     B                                                       ______________________________________                                        SHAPE             Trilobe Present Invention                                   DIMENSIONS (in.)                                                              d.sub.1           .048    .048                                                d.sub.2           .052    .068                                                1                 .149    .152                                                lobe radius       .013    .013 (r.sub.2)                                      Test Support Span* (in.)                                                                        .026    .042                                                CRUSH STRENGTH                                                                lb/mm length      4.6     4.4                                                 Standard Deviation (lb.)                                                                        1.4     1.4                                                 ______________________________________                                         *Horizontal, unsupported distance over which crushing force was applied       perpendicularly                                                          

The invention is claimed as follows:
 1. A catalyst particle comprisingone or more hydrogenation metals selected from Group VIB and Group VIIIof the Periodic Table of Elements and a porous, inorganic oxidesubstrate supporting said metal or metals, said particle having agenerally cylindric configuration with a cross-section of trilobularshape having concave interlobular interstices bluntly rounded withgreater curvature than the curvature of the lobes, wherein thetrilobular shape is defined by an equilateral triangle, the midpoints ofadjacent sides of the triangle serving as the centers for twolobe-defining radii of curvature (r₂), the vertices of the triangledefining the centers for the interstitial radii of curvature (r₁), andthe common intersection of the bisectors of the included angles of thetriangle serving as the center for the remaining lobe-defining radius ofcurvature (r₃).
 2. A catalyst particle according to claim 1 wherein r₂<r₃ <r₁.
 3. A catalyst particle according to claim 4 wherein r₂ is atleast about 0.012 inches.
 4. A catalyst particle according to claim 1wherein the trilobular cross-section is circumscribed by a rectangle andwherein the cylindric height (L) of the particle is about 2.5 to about 4times the small dimension (d₁) of the rectangle.
 5. A catalyst particleaccording to claim 1 wherein the trilobular cross-section iscircumscribed by a rectangle and wherein the smaller dimension (d₁) ofthe rectangle is equal to about 70% of the greater dimension (d₂) of therectangle.